Image scanner

A scanner ( engl. to scan, scan ') or sampler is a data acquisition device that scans or missing an object on a systematic and regular manner. Scanning is an opto- mechanical process.

The main idea is to generate a relatively limited measurement instruments by a multitude of individual measurements, a total image of the object.

The scanner picks up the analog data of the physical template with the help of sensors and translates them then with A / D converters in digital form. So for example they can be processed with computers, are analyzed or visualized.

• 2.1 Scan with color filters
• 2.2 Scan with colored light sources
• 2.3 Scan with a white light source

Scanner types

3D scanner

Three-dimensional templates can be read only with a 3D scanner. One uses such devices mostly for cataloging or archiving objects. The downside is that the scanning device often permanently mounted must be or reference points need to be glued to the object at hand scanners.

Book Scanner

A book scanner is used primarily for reading Scripture bound documents. Special versions also allow scanning of loose documents, records and maps.

Slide scanner

The type of scanner is used in both professional and semi-professional range and is available in two versions: one as a pure film scanner in which by means of special devices, the slides and negatives into the scanner are performed, and on the other as a hybrid device in which a flatbed scanner receives a special Transparency Unit. For both versions there are both simple as well as sophisticated instruments, which differ greatly in addition to the pixel density in the density range. The optical resolution of high-quality equipment is approximately 3000 ppi to 4000 ppi. In addition, they also work with a special illumination method to eliminate the usual scatter and side effects while scanning reflecting material. See also for slide scanning.

Document Scanner

For the acquisition of large quantities of records flatbed scanner with ADF (Automatic Document Feeder), fed scanner or special high- speed scan roads are used as document scanners.

Transmitted light scanner

Transmitted light scanners are used in transparent materials such as films, slides, x-rays.

Faxes

Each fax machine has a sheet-fed scanner for its transmission direction. Here, a line of light-sensitive CCD sensors ( sensors or other technology) is built into the device. The template is passed along it. During fax pure monochrome operation is used, ie recognized neither color nor grayscale.

Fed scanner

The sheet-fed scanner is constructed just like a fax machine (see above ), but now in addition to grayscale, and color recognition. The obvious disadvantage of feed scanner is the exclusive processing of single documents or batches of it. Books can not be scanned. It can also lead to unpleasant edge distortion when moving smooth styles, such as photos. They are mainly in the enterprise space as a document scanner for use.

Document reader

To read mostly smaller documents (for example, by hand, by ticking filled forms ), otherwise in the art such as document scanners or debit scanners.

Film scanner

In contrast to transmitted light flatbed scanners come with a film scanner film scanning of photographic material such as film negatives, slides and motion picture films for television and cinema purposes for use. See also film scanner.

Flatbed Scanner

The flatbed scanner, which is now most commonly used imaging device, works on the same principle as a copy machine. The template is placed on a glass sheet, it remains always at the same place, the photosensitive sensors are led along during scanning of the glass sheet. This method allows, in addition to photos and images to scan bulky originals such as books. To achieve a sharp image, the object must lie completely flat on the glass plate. However, this causes problems with some templates. Cost flatbed scanner can scan originals up to A4.

Large Format Scanner

Upon submission of sizes greater than A2 one speaks of large format scanners, which are offered as swipe, flatbed or drum scanner. When pulling scanners there are two competing systems, CCD and CIS. CCD works with several small camera sensors ( hence the name). Similar to panoramic images, the image of the cameras will be charged to an overall picture. The reflected light from the document is getting collimated by mirrors and lenses on the sensor. CIS ( Contact Image Sensor ) works with sensor strip on the incident, the reflected light from the document directly. Given in the CIS technique, several sensor strip the entire scan width, a focusing of the light through lenses is not necessary and there are fewer defects (no offset between the cameras, low distortion and no color fringing ). For the CIS technology is prone to blurring when irregularities of the scan template.

Handheld Scanner

As the name suggests, you have to pull the hand scanner by hand on the submission. One must not subject the scanner to quickly pull on the submission ( because a certain limit for the computer transmitted data amount can not be exceeded ) and should it carry out any lateral deviations from the straight line, what and by a wide, parallel to the ( one-dimensional linear ) scan mounted roller is supported. These are recognized in connection with a pulse generator and the distance traveled on the template and so that the second dimension. To scan an A4 page, you have to scan several times, because the units are too narrow. Hand scanners were early popular until the mid-1990s, but have long since disappeared from the market because of its disadvantages and the sharp drop in prices for flat -bed scanner.

Radar

The rotating, horizontal strongly converging antenna of a panoramic view of the radar is sometimes referred to as a scanner. Along with the presentation on vector-oriented screens that belongs to the radar imaging process.

Réseauscanner

Scanner for applications in photogrammetry as Réseauscanner

Scanner in medicine

In medicine, there are different scanners, such as

• Computer tomography, Digital volume tomography

Drum scanner

This is one of the oldest types of scanners, but still provides the most accurate results. Resolution (about 12,000 ppi), speed and quality remain unmatched by other types of equipment. The drum scanner of the former world leader Heidelberg printing machines are equipped with the special software SilverFast still used on modern computer systems. The drum scanner, the original is mounted on a rotating drum, in which the illumination and scanning system of linearly moved past so that the original is scanned helically. Because the light source and the scanning system is always in the same position on the paper, can be achieved with simple means an excellent quality. In addition, drum scanners have instead of the normal CCD sensors highly sensitive photomultiplier for reading the data. The disadvantage is that they cost a lot and are very large. An early use of drum scanners was telegraphy.

Operation of a scanner

Scanners usually work on the following principle: The original image is illuminated and the reflected light is directed through a rod lens, which is to focus the reflected light and eliminate the scattered light in an optoelectronic line sensor ( quick scan, English: fastScan ). The analog light signals are converted pixel by pixel by analog - to-digital conversion to digital signals while simultaneously operating either the template or the sensor optics is moved stepwise perpendicular to the sensor extension (slow scan, english: slow scan).

When scanning with an area sensor, the entire template or areal parts of the image can be scanned simultaneously.

The repeated scanning after displacement of the sensors in the sub-pixel image resolution and possibly the photographic resolution can be increased.

Scan with color filters

Certain color values ​​are separated by sampling the primary colors ( usually red, green and blue ) with Upstream of color filters and, if determined by software-based, additive color mixing. This filter process required for each primary color a scan cycle when all of the sensor elements are used for the scan. Alternatively Bayer sensors or other color sensors are used, in which all sensor elements are each provided with a fixed color filter in a predetermined color order. This allows the scan to be performed in one pass (see CCD).

Scan with colored light sources

The use of multi colored and switchable light sources only one scan pass is needed because the color separation is given by the light sources themselves. The sensors measure during a measurement, for example, with lighting by low-cost LEDs only light of a certain wavelength ( see also CIS). Alternatively, colored light sources with a continuous light spectrum can be used.

Scan with a white light source

In the prism method the original is illuminated with white light. The reflected light is passed through a prism which splits the color components. These are covered by adjacent optical sensors. With this technology, only one scan is required.

Scanner Features

The quality of a scanner is depending on the application depends on:

• Sampling resolution and sampling frequency or spatial frequency
• Screen frequency
• Output frequency ( output resolution )
• Density range ( dynamics)
• Tonal ( shades of gray)
• Color depth
• Scan speed

Simple scanner with an ADF process about ten pages per minute. High-performance scanner with a mechanism for turning collect 40 pages of a book per minute.

Quality characteristics

The quality of scanners can often by means of a so-called cavity effect ( english cavity effect) estimated. This dice are made ​​of black cardboard scanned with about ten centimeters on a side and a hole of about five millimeters in diameter on the side of the hole. The hole side can be modified so that it is outside of white cardboard. The hole is approximately represents a blackbody radiator which emits practically no visible light. In the scan therefore likely to be present at the location of the hole is no signal.

In practice, however, still occur signals, which essentially have two causes:

• Murmur
• False light

The latter is thus concluded that light from the surroundings of the hole is scattered in the imager scanner and represents the cavity effect Represents the noise is stationary essentially independent and therefore has a constant level.

The following eight sample images to illustrate these effects. The first four represent the original measurements, whereas the next four images are provided with a gamma correction. On the left side a good scan and on the right a bad scan is shown in each case. The upper images show a perforated cube full of black cardboard and the lower one with a white perforated outer surface.

In the two bottom right images significant artifacts can be seen. In the upper right picture that has been scanned with black cardboard, can be clearly seen the image noise in the hole. In the lower right image, this noise is still visible in the center, but is outshined by false light which is weaker toward the center of the hole.